The planet is one of the nearest exoplanets to Earth that can be seen crossing the face of its star, and has been intensively studied by Hubble and other telescopes.

Exoplanets are celestial bodies which orbit stars other than our own Sun.

“Measuring its colour is a real first – we can actually imagine what this planet would look like if we were able to look at it directly,” said Frederic Pont of the University of Exeter, who co-wrote the paper in Astrophysical Journal Letters.

Professor Pont and a team measured how much light was reflected off the planet’s surface, a property known as albedo, in order to calculate its colour.

The blue comes not from the reflection of a tropical ocean, as in Earth’s case, but a hazy, turbulent atmosphere believed to be laced with silicate particles – the stuff of which glass is made.

These particles scatter blue light.

HD 189733b is an example of a “hot Jupiter” planet, similar in size to the gas giants in our own solar system but closer to their parent star.

“It’s difficult to know exactly what causes the colour of a planet’s atmosphere, even for planets in the Solar System,” Professor Pont said.

“But these new observations add another piece of the puzzle over the nature and atmosphere of HD 189733b.

“We are slowly painting a more complete picture of this exotic planet.”

So far, no exoplanet spotted has the potential to be a home away from home; a rocky planet that orbits in a balmy zone, enabling water to exist in liquid form and thus nurture life as we know it.